Recommendation? diy heat oven

P

prodago

Joined
Dec 22, 2016
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i'm trying to build a heat treating oven that will reach 2000°F. I have 16 gauge kanthal coils which I made. I'm going to be coming from 120 V power source and the coils I have a resistance of 20 ohms so will this work?
 
V-IR
120=Ix20
I= 6 amps
P=VI 720 watts

That won't get hot enough. To reach 2000°F you need around 13amps to get 1550 watts on 120VAC. That would require a coil with around 9 ohms.
 
so if i shorten the coil, will that work? if not what can i do to reach that temp?
thanks for your reply
 
prodago said:
so if i shorten the coil, will that work? if not what can i do to reach that temp?
thanks for your reply
Click to expand...
The wattage is only one part of the equation, a lot will depend on the size of the furnace and on insulation. What is the volume of your chamber?
 
prodago said:
18" long x 6" tall sides
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How wide is it on the inside? Take a look at Dan Comeau's page about DIY heat treat ovens if you have not already. He has a table showing wattage per cubic foot for common heat treat ovens. I think the one I built has about 7kW/ft^3. I don't recall the exact time it takes to get to the temperature you are looking for, but I typically plan to let it preheat for at least an hour for AEB-L.
 
Hubert S. said:
How wide is it on the inside? Take a look at Dan Comeau's page about DIY heat treat ovens if you have not already. He has a table showing wattage per cubic foot for common heat treat ovens. I think the one I built has about 7kW/ft^3. I don't recall the exact time it takes to get to the temperature you are looking for, but I typically plan to let it preheat for at least an hour for AEB-L.
Click to expand...
those dimensions are the inside
 
Hubert S. said:
Sorry about the misunderstanding. You only gave the internal length and height, not enough to compute the volume. That's why I asked about the width on the inside.
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sorry man, My wife says that my communication skills suck! 18 inches long and 6 inches on the sides the back, front and width.
hope this helps.
thanks for replying
 
Ok, so your volume is 0.375 ft^3. If you go with Stacy's suggestion above, you'll be around 4 kW/ft^3. I guess that can work with good insulation, but it is on the low end of commercial offerings. I would not expect it to be really fast and it may struggle to get to the 2,000°F you are targeting. Do you have any 20 Amp outlets? They look like regular outlets, but have one T-slot, see picture from wikipedia.org below (that picture is upside down compared to what you'll typically see in a house in the US). With that you could get a little more power without a 220 V outlet. The downside to doing that is that you increase the surface load on the elements and they might not last as long.

799px-Electrical_outlet_with_label.jpg
 
Texas has 220. Check the breaker box. You might have to add an outlet, but the panel is almost surely 220.

Hubert ( and others),
Plugging into a 20 amp outlet does not deliver 20 amps to a device. The device will only draw the current that is required by its resistance. Plug in a 100 watt light bulb and it will draw .83 amp. Plug in a 1000 watt heater and it will draw 8.33 amps. His coil is 20 ohms, which will draw only 6 amps regardless of where it s plugged in.
Shortening the coil by half will cut the resistance by half, and double the amps - which should work, if he wound the coil at the right size.

Normally, it is best to order a pre-wound coil that has a desired resistance and length. 15 to 17 gauge is the right size wire for most HT oven builds. You want a coil that draws around 16 amps for a 120VAC oven.
 
Stacy E. Apelt - Bladesmith said:
Texas has 220. Check the breaker box. You might have to add an outlet, but the panel is almost surely 220.

Hubert ( and others),
Plugging into a 20 amp outlet does not deliver 20 amps to a device. The device will only draw the current that is required by its resistance. Plug in a 100 watt light bulb and it will draw .83 amp. Plug in a 1000 watt heater and it will draw 8.33 amps. His coil is 20 ohms, which will draw only 6 amps regardless of where it s plugged in.
Shortening the coil by half will cut the resistance by half, and double the amps - which should work, if he wound the coil at the right size.

Normally, it is best to order a pre-wound coil that has a desired resistance and length. 15 to 17 gauge is the right size wire for most HT oven builds. You want a coil that draws around 16 amps for a 120VAC oven.
Click to expand...
Of course, plugging into a different outlet does not change the current draw of a device, that goes without saying. I suggested to look for a 20 Amp outlet so the OP can design his coil to draw more current. I am not an electrician, but the 16 A draw you suggest seems too high for a typical 15 A outlet.
 
OK, I just didn't want the OP or others thinking you just plug it into a higher amp socket. Many homes have a 20 amp breaker for the garage, or an air conditioner. The clothes washer is often 20 amp and an electric dryer is usually 220-30 amp. These are places or circuits that you can find the needed curent/voltage.

Caution:
People sometimes just change the breaker to get a 20 amp circuit. This is WRONG and can start a fire. It is actually illegal. The wires are of a gauge that matches the breaker. Unless you or a qualified electrician have ascertained that the wiring is 12 gauge, never change a 15 amp breaker for a 20 amp one.
 
Hubert S. said:
Ok, so your volume is 0.375 ft^3. If you go with Stacy's suggestion above, you'll be around 4 kW/ft^3. I guess that can work with good insulation, but it is on the low end of commercial offerings. I would not expect it to be really fast and it may struggle to get to the 2,000°F you are targeting. Do you have any 20 Amp outlets? They look like regular outlets, but have one T-slot, see picture from wikipedia.org below (that picture is upside down compared to what you'll typically see in a house in the US). With that you could get a little more power without a 220 V outlet. The downside to doing that is that you increase the surface load on the elements and they might not last as long.

799px-Electrical_outlet_with_label.jpg
Click to expand...
WOW. thanks.
 
Ok, just want to add one more thing regarding safety. If you design the furnace for a 20 Amp outlet, use the proper plug so it cannot be plugged into a standard 15 Amp outlet. The designation for the plug is NEMA 5-20P.
 
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